Dresden 2009 – scientific programme
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O: Fachverband Oberflächenphysik
O 36: Particles and clusters
O 36.1: Talk
Wednesday, March 25, 2009, 15:00–15:15, SCH A01
Nature of Ar bonding to small CoN+ clusters and its implications for the structure determination by far-infrared absorption spectroscopy — •Ralf Gehrke, Philipp Gruene, André Fielicke, Gerard Meijer, and Karsten Reuter — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany
Far-infrared vibrational spectroscopy by multiple photon dissociation has proven to be a very useful technique for the structural fingerprinting of small metal clusters [1]. Whereas previous work on cationic vanadium clusters assumed a negligible influence of the adsorbed Ar probe atoms, measured vibrational spectra of small cationic cobalt clusters show an intriguing dependence on the number of adsorbed Ar atoms, which becomes stronger with decreasing cluster size. Focusing on Co4+ to Co8+ we therefore use density-functional theory to analyze the Ar-CoN+ bond and its role for the IR spectra. First, low-lying isomers are identified through first-principles basin-hopping runs. A comparison of their computed spectra with the experimental data then enables in some cases a unique assignment of the cluster structure. Independent of the specific isomer, we obtain a pronounced increase of the Ar binding energy for the smallest cluster sizes, which correlates with the observed increased influence of the Ar atoms on the IR spectra. Further analysis of the electronic structure motivates an electrostatic picture that not only explains this binding energy trend, but also why the influence of the rare-gas atom is much stronger than in the previously studied systems. [1] A. Fielicke, A. Kirilyuk, C. Ratsch, J. Behler, M. Scheffler, G. von Helden, G. Meijer, Phys. Rev. Lett. 93 (2), 023401 (2004)